Situation · DIY
Drafts, water or daylight under the garage door: which seal to fix
A closed door has several gaps and each takes a different seal. How to tell which one failed, what each costs, and where insulation fits.
What you’re seeing and hearing
- Daylight under the closed door, leaves blown in after a windy week, or the heater running longer than it should. Source: The best garage door weather seal
- Daylight at the corners but not the middle: the slab isn’t flat, and a new bottom seal alone won’t close that. Source: The best garage door weather seal
- A draft along the sides or top with no visible gap: the jamb seal has stiffened in the sun while still looking fine. Source: The best garage door weather seal
Is it safe to use the door right now?
Yes. A failed seal costs comfort and energy, not safety.
- Air leaking at the bottom, sides and top bypasses the door’s insulation entirely: an R-18 door can lose most of its benefit to a failed bottom seal. Source: Garage door insulation R-value explained
DIY or a pro, and why
Yours: three seals, each a weekend job.
- Bottom U-seal: slides into the retainer along the bottom of the door. Match the retainer profile (T-style, bead or P-bulb). Source: The best garage door weather seal
- Threshold seal: bonded to the floor, for a slab that has sloped or settled. It needs clean, dry concrete above freezing to cure. Source: The best garage door weather seal
- Jamb weatherstripping: the flap on the sides and top of the opening, pressing lightly on the door. It needs a miter saw and galvanized finish nails. Source: The best garage door weather seal
- To test the jamb seal, run a lit incense stick along it on a windy day with the door closed. If the smoke pulls, the seal is gone. Source: The best garage door weather seal
What the fix involves and costs
- A bottom seal lasts five to ten years before it loses its compression memory: it goes chalky, cracks, or stays flat and stops springing back. Source: The best garage door weather seal
- The jamb seal lasts ten to fifteen years with moderate sun. Source: The best garage door weather seal
- Insulation is a separate question: a single-skin steel door is about R-0 and a polyurethane-injected one R-12 to R-18. For a detached, unconditioned garage, going past R-12 buys little. Source: Garage door insulation R-value explained
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